This paper presents the current research on impedance-based structural health monitoring technique at the Center for Intelligent Material Systems and Structures. The basic principle behind this technique is to apply high frequency structural excitations (typically higher than 30 kHz) through the surface-bonded piezoelectric transducers, and measure the impedance of structures by monitoring the current and voltage applied to the piezoelectric transducers. Changes in impedance indicate changes in the structure, which in turn can indicate that damage has occurred. Three examples, including a bolted joint, gas pipeline and composite structure, are presented to illustrate the effectiveness of this health monitoring technique to the wide variety of practical field applications. Although many proof-of-concept experiments have been performed using the impedance methods, the impedance-measuring device (HP4194A) is still bulky and expensive. Therefore, we have developed an operational amplifier-based turnkey device that can measure and record the electric impedance of a PZT. The performance of this miniaturized and portable device has been compared to our previous results and its effectiveness has been demonstrated. This paper summarizes the experimental setup, procedures, considerations needed to implement the device in field applications.